The present invention relates to viewing screens, and more particularly, to a novel method for fabricating a viewing screen with enhanced contrast, and the screen so formed.
Rear projection viewing screens are utilized in rear projection television and the like systems, wherein the amount of light which can be projected upon the viewing screen is limited by the brightness of phosphors presently available. Contrast of the image thus formed will decrease with increasing levels of ambient light reflected to a viewer, from darker areas of the screen image. Thus, ambient light must be severely reduced to prevent the appearance of a "washed out" image on the screen.
Typically, to prevent ambient light reflection to the viewer, the material of which the projection screen is fabricated often includes a bulk darkening agent. The bulk darkening agent absorbs some of the ambient light, but also absorbs a portion (typically about 20%) of the light to be transmitted through the screen to the viewer. Thus, the viewer sees an apparently dark screen having an increase in contrast under ambient light conditions; this apparent increase in contrast is offset by the attenuation of brightness, i.e. the reduced magnitude of light transmitted through the screen.
It is also known to provide improved contrast by casting lenslets into one of the surfaces of a screen, whereby light is focused on the viewable screen surface, so that less than one-half of that surface actually transmits light. The remainder of the screen surface is blackened, presenting a very dark appearance to the viewer but providing improved contrast. However, the fabrication of a screen having cast lenslets, wherein the lenslets are curved in both dimensions of the screen plane, is both difficult and costly. It is therefore highly desirable to provide a projection screen in which an improved contrast ratio can be provided in more economical manner than hitherto known screens.